How do I get rid of the small line that appears in-between offsets when using array?
Ideally, you need to go back a step and fix the Array. It should be 'Relative' offset, by '1' in X, and 'Merge' should be checked, so the array elements become continuous. But before you do that, you have to remove the faces at the element ends, that coincide where they join, otherwise there will be internal faces in the array. There will be no need to apply the array, you can leave the modifier live.
After doing that, and Simple Deform &gt; Bending your array, there may still be a join visible where its ends meet at 360 degrees. You can get rid of that with a Weld modifier.
It may be worth going into the object's Data tab &gt; Normals panel, to give the whole object an 'Autosmooth', set to about 45 degrees.
Your .blend had the Array applied, so I couldn't fix that. I repaired the mesh instead. But really, you should go back. It's better to keep your modifiers alive as long as possible, for flexibility.